It has been determined that a set of genes present in various strains of retroviruses are responsible for tumors in animals. Sequences homologous to these oncogenes can be found in normal cells of most animals from invertebrates up to and including man. Due to their highly conserved sequences and wide distribution, it has been suggested that these genes play some essential role in the maintenance of cells and that an alteration either in the sequence or the level of expression may cause abnormal cell growth which would result in tumor formation. As our overall objectives we are in the process of determining which, if any, of these genes may be involved in human leukemias and what functions these highly conserved genes have in normal cells. We will determine whether the level of expression of several known hematopoietic-associated oncogenes in highly characterized childhood leukemia cells is abnormal as compared to levels in normal hematopoietic cells at the same stage of differentiation. To accomplish this we will employ in situ hybridization techniques to observe oncogene RNA levels in morphologically identifiable cells. In addition, we will determine whether oncogenes or their surrounding chromosomal environment are altered as compared to normal cells. This will involve (1)\determining the chromosomal position of several oncogenes by in situ hybridization and comparing these locations to translocations, deletions and insertions observed in tumor cells, (2)\analyzing the gross nucleic acid sequence around the oncogenes by restriction endonucleases for insertions and deletions, and (3)\observing methylation patterns of the oncogenes which may indicate altered controls. Finally, we will determine whether one or more oncogenes are involved in the formation of specific leukemias. This investigation will employ transfection assays using a variety of recipient cells and will eventually provide new oncogene probes with which to analyze expression of genes known to possess oncogenic activity.